Mobile communication systems have been greatly advanced through first generation analog-type advanced mobile phone systems (AMPS) and second generation cellular/personal communication service (PCS) systems. Recently, international mobile telecommunication-2000 (IMT-2000) systems have been developed and are widely used as third generation high-rate data communication systems.
IMT 2000 services may be classified into a Code Division Multiple Access (hereinafter, referred to as a CDMA) 2000 1X services and CDMA 2000 1x EV-DO services.
The CDMA 2000 1X service enables a wireless Internet to be provided at a speed of 144 kbps at maximum, which is far faster than a speed of 14.4 kbps or 56 kbps supported by the existing IS-95A/B networks, by means of IS-95C network upgraded from the IS-95A/B networks. Accordingly, the service quality of the existing voice and Wireless Application Protocol (WAP) can be improved through the CDMA 2000 1x service. In addition, various multimedia services (e.g., AOD, VOD) can be provided.
The 3GPP2 (3rd Generation Partnership Project2), which is a collaborative international standardization group, offers standards for a CDMA IMT-2000 system as IMT-2000 standards in order to provide multimedia mobile communication services. According to the above standards, a high rate packet data system called “CDMA 2000 1x EV-DO (evolution data optimized)” based on an HDR (high data rate) proposed by Qualcom Incorporated, has been decided upon as an international standard high rate packet data system. A CDMA 2000 1xEV-DO (hereinafter, referred to as ‘1xEV-DO’) system has been upgraded from a CDMA 2000 1X system and is designed to transmit only data.
The 1X system utilizes both circuit networks and packet networks and provides single directional low-rate data services with a maximum transmission rate of 307.2 Kbps as well as voice data. In contrast, the 1xEV-DO system is dedicated for a packet network and provides bi-directional high-rate data services with a maximum transmission rate of 2.4 Mbps.
In the following description, the CDMA 2000 1X system is simply referred to as “1X system” and the CDMA 2000 1xEV-DO system is simply referred to as “1xEV-DO system” for the convenience of explanation.
Currently, the 1xEV-DO system has been used together with the conventional 1X system. That is, both of the 1xEV-DO system and the conventional 1X system are installed in one wireless base station or a base station controller even though they are operated separately from each other. In other words, a transceiver of the wireless base station includes a channel card for the 1xEV-DO system and a channel card for the 1X system, respectively. In addition, the base station controller includes a data processing board for processing packet data transmitted/received through a 1xEV-DO system and another data processing board for processing data transmitted/received through a 1X system, respectively.
When high-rate data (i.e., multimedia data) are transmitted to a mobile communication terminal from a mobile communication system, such as the wireless base station or the base station controller, the data are transmitted through the 1xEV-DO system. In addition, voice signals or low-rate data are transmitted through the 1X system.
A hybrid access terminal is a mobile communication terminal capable of receiving communication services transmitted from both the 1xEV-DO system and the 1X system. Further, the hybrid access terminal may periodically and alternately monitor each of the 1xEV-DO and 1X systems in a predetermined period of time. That is, in a 1X mode in which the 1xEV-DO system is not used, the hybrid access terminal making communication with the 1X system periodically searches the 1xEV-DO system. Further, when the hybrid access terminal is in traffic with the 1xEV-DO system, the hybrid access terminal periodically searches the 1X system while making communication with the 1xEV-DO system.
For instance, the hybrid access terminal in traffic with the 1xEV-DO system responds to call signals, such as voice call-accepted signals and short messages, which may be transmitted to the hybrid access terminal from the 1X system. Further, the hybrid access terminal periodically accesses to the 1X system to register its own position to the 1X system, receives overhead messages such as system parameter messages and access messages and updates system resources.
However, the hybrid access terminal must stay in the 1X system until the system resources have been completely updated whenever the hybrid access terminal periodically accesses to the 1X system even if the hybrid access terminal is in traffic with the 1xEV-DO system.
In addition, the 1xEV-DO system may perform a call drop operation if a signal having a level below a predetermined level is received from the hybrid access terminal through a data rate control (DRC) channel when the hybrid access terminal is in traffic with the 1xEV-DO system for a predetermined period of time (designated as a parameter in the system). That is, regardless of reasons thereof, if the signal having the level below the predetermined level are received through a reverse channel for a predetermined period of time, the 1xEV-DO system performs the call drop operation with respect to the hybrid access terminal in order to efficiently utilize the system resources.
However, currently used 1xEV-DO systems have structures which do not provide a user with reasons for the call drop operation. In other words, the 1xEV-DO system does not provide the user with information allowing the user to find a precise reason for the call drop operation, even though the call drop operation may happen in various situations, such as when the hybrid access terminal making a call-connection with the 1xEV-DO system is shifted into a wave shadow zone, when a communication system malfunctions, or when the hybrid access terminal is switched into the 1X system.